1. Field of the Invention
The present invention is directed to a dry shaver with at least one floatingly supported cutter head.
2. Description of the Prior Art
U.S. Pat. No. 5,189,792 discloses a dry shaver in which a cutter head is floatingly supported from a head frame to be capable of being depressed in response to the cutter head being pressed against the skin of a user. The cutter head comprises a holder carrying an outer foil and an inner cutter driven to reciprocate in shearing contact with the outer foil. The inner cutter is urged by a spring against the outer foil to give a suitable contacting pressure therebetween. An elastic support member is provided to give an elastic force for floatingly supporting the holder to the head frame. Thus, the cutter head is floatingly supported to the frame by the combination of a biasing force from the spring and an elastic force from the support member. The elastic support member comprises a resilient beam which exhibits a fixed elastic constant substantially over the depression displacement of the holder relative to the head frame. Consequently, the cutter head carrying the outer foil is floatingly supported with the combination force with a fixed elastic constant having a linear relation between the displacement of the holder and a depression load applied thereto, as indicated by a line L1 in FIG. 9. In the meanwhile, it is found that a comfortable and effective shaving is achieved by changing elastic constant of the supporting structure for the cutter head in such a manner that the cutter head can be initially depressed with a less depression load than when depressed to nearly the end of its depression stroke. That is, the cutter head is preferred to be supported with elastic constant which is lower in the initial depression stroke than otherwise so that it can conform readily to an irregular skin surface with a less depression load for smooth and effective shaving. Such floating support should be made without greatly varying the contacting pressure between the inner cutter and the outer foil for assuring a smooth shaving substantially irrespective of the varying depression amount of the cutter head. In this respect, the shaver of the above patent is not sufficient to give an optimum characteristic to the shaver required for assuring comfortable and effective shaving.
Japanese Utility Model Publication (KOKOKU) No. 48-57291 discloses another prior shaver in which a cutter head is floatingly supported from the head frame singly by a spring which urges the inner cutter to the outer foil. In this shaver, the contacting pressure between the inner cutter and the outer foil increases in direct proportion to the depression displacement. Therefore, the contacting pressure will increase beyond a suitable value when the cutter head is depressed by a large extent. Otherwise, the cutter head is movable only by a limited displacement when it is intended to maintain the contacting pressure within an acceptable range.
A further prior shaver is disclosed in GB 1 281 835 in which a plurality of concentric cutter heads are supported by individual springs which urges the inner cutters receptively against the corresponding outer foils. The springs are arranged such that the center cuter head receives a biasing force from its associated spring plus the biasing forces for the other cutter heads. Thus, the center cutter head can be depressed by a large extent only with accompanied displacement of the other cutter heads. In view of that the individual springs are required to give a suitable contacting pressure between the individual inner cutters and the associated outer foils, when the center cutter head is depressed by a large extent with the accompanying depression of the other cutter head, the center cutter head will have to give a considerably great floating force which is a combination with the floating force of the other cutter heads being pressed. With this result, the center cutter head sees an abrupt increase of the biasing force, which eventually fails to give a moderate contact between the center cutter head and the skin of the user, and therefore reduce shaving efficiency.